Segment Reporting - Segment Reporting Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Revenues:
Revenues	$ 968.3	$ 968.3
Costs of services	701.7	692.9
Gross Profit:
Total Gross Profit	266.6	275.4
Selling, general, and administrative expenses	224.4	214.5
Amortization of intangible assets	14.5	14.3
Operating income	27.7	46.6
Interest Expense, Operating and Nonoperating	17.1	15.4
Income before income taxes	10.6	31.2
Provision for income taxes	5.1	10.3
Net income	5.5	20.9
Commercial
Revenues:
Revenues	675.5	672.2
Federal Government
Revenues:
Revenues	292.8	296.1
Operating Segments [Member]
Revenues:
Revenues	968.3	968.3
Costs of services	701.7	692.9
Gross Profit:
Total Gross Profit	266.6	275.4
Other Depreciation and Amortization	12.9	10.5
Other Expenses	177.4	175.7
Selling, general, and administrative expenses	190.3	186.2
Amortization of intangible assets	14.5	14.3
Operating income	61.8	74.9
Operating Segments [Member] | Commercial
Revenues:
Revenues	675.5	672.2
Costs of services	466.3	454.5
Gross Profit:
Total Gross Profit	209.2	217.7
Other Depreciation and Amortization	11.0	9.0
Other Expenses	150.8	146.0
Selling, general, and administrative expenses	161.8	155.0
Amortization of intangible assets	8.8	7.8
Operating income	38.6	54.9
Operating Segments [Member] | Federal Government
Revenues:
Revenues	292.8	296.1
Costs of services	235.4	238.4
Gross Profit:
Total Gross Profit	57.4	57.7
Other Depreciation and Amortization	1.9	1.5
Other Expenses	26.6	29.7
Selling, general, and administrative expenses	28.5	31.2
Amortization of intangible assets	5.7	6.5
Operating income	23.2	20.0
Segment Reporting, Reconciling Item, Corporate Nonsegment [Member]
Gross Profit:
Corporate SG&A Expenses	$ 34.1	$ 28.3